#include <iostream>
using namespace std;
class Point {
    friend class Triangle;
    double x;
    double y;
public:
    Point()
    {

    }
    Point(double x1, double y1)
    {
        x = x1;
        y = y1;
    }
    Point(Point& p);
    double getx()
    {
        return x;
    }
    double gety()
    {
        return y;
    }

};
Point::Point(Point& p) {
    x = p.x;
    y = p.y;
}
class Triangle {
    Point p1;
    Point p2;
    Point p3;
public:
    Triangle(Point p1, Point p2, Point p3) :p1(p1), p2(p2), p3(p3)
    {
    }
    double getArea() {
        double s;
        s = (p2.y * p3.x) / 2;
        return  s;
    }
};
int main() {
    double x, y;
    cin >> x >> y;
    Point a(x, y);
    cin >> x >> y;
    Point b(x, y);
    cin >> x >> y;
    Point c(x, y);
    Triangle t(a, b, c);
    cout << t.getArea() << endl;
    return 0;
}